Cancelled policy but still debit

I had a a car insurance with top up insurance it Regent. I called to cancel the insurance policies but only the car insurance was cancelled not the top up. I called again to inquire why the the top up was not cancelled and I was told to write a separate letter for that which I did on the 2 November 2017. To my surprise the top up policy is still being debited on my bank account even though I cancelled it.